Quick start

This page computes the alpha-particle loss fraction of a public quasi-axisymmetric reactor-scale VMEC equilibrium (Landreman and Paul 2022, from the simsopt test files) with examples/simple.in.

Run

From the repository root, after Installation:

mkdir -p run
cp examples/simple.in run/
curl -L -o run/wout.nc https://github.com/hiddenSymmetries/simsopt/raw/master/tests/test_files/wout_LandremanPaul2021_QA_reactorScale_lowres_reference.nc
cd run
../build/simple.x simple.in
examples/simple.in
&config
trace_time = 1d-2        ! slowing down time, s
sbeg = 0.3d0             ! starting s (normalzed toroidal flux) for particles.
ntestpart = 128          ! number of test particles
netcdffile = 'wout.nc'   ! name of VMEC file in NETCDF format
isw_field_type = 2       ! -1: Testing, 0: Canonical, 1: VMEC, 2: Boozer, 3: Meiss, 4: Albert
/

The run traces 128 alpha particles of 3.5 MeV for 10 ms, started on the surface \(s = 0.3\) (normalised toroidal flux) with random angles and uniformly random pitch \(\lambda = v_\parallel/v\). isw_field_type = 2 integrates in Boozer coordinates. All other keys keep the defaults of examples/simple_full.in. The run takes 20–30 s on a workstation; most of it is field setup, which the log reports phase by phase.

Result

tail -1 confined_fraction.dat

1.0000000000000000E-002  0.70312500000000000  0.29687500000000000  128

The columns are time (s), confined fraction of passing markers, confined fraction of trapped markers and the number of numerically resolved markers. The loss fraction at 10 ms is \(1 - f_\text{pass} - f_\text{trap} = 0\): no marker left the plasma. Starts are random, so another run differs; in this optimised configuration 0 to a few of 128 markers are lost. Add deterministic = .true. for a fixed seed.

orbit_exit_code.dat shows code 3 for about half of the markers: deeply passing markers (trapping parameter \(\le\) contr_pp) are counted as confined without tracing. times_lost.dat holds the loss time and end state of every marker. Outputs describes all files and codes.

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